Geographical and Genetic Heterogeneity during Speciation

有时，同一物种内的种群开始利用不同的资源或栖息地。随着时间的推移，如果某一种可能资源的专家比一般人留下更多的后代，这些种群就会在基因上产生分歧。如果这种特殊的资源使用改变了配偶选择的模式，使得个体倾向于与使用相同资源或栖息地的其他个体交配，那么这些不同的种群可能会变成两个不同的物种。尽管在遥远的过去，在地球上数以百万计的物种中可以清楚地看到许多物种形成的产物，但在不同的种群中重建物种形成的过程是困难的，因为物种形成完成后，这一过程的重要线索就消失了。首先，不同地理位置的不同种群对各种资源的自然选择是半独立的——它们可能以不同的速度接近物种形成，甚至朝着不同的结果进化。其次，在不同的自然选择下，早期物种内部的一些基因分化非常迅速，这些基因组区域的分子变异模式讲述了物种形成的遗传故事。然而，随着时间的推移，这些独特的模式变得模糊了，最终所有的基因都将讲述同样的故事，因此对古代分化物种的分析无法确定驱动这一过程的关键基因变化。在这里，一组经过充分研究的昆虫物种（豌豆蚜虫）的种群，它们专门针对不同的寄主植物，将被用来捕捉物种形成的早期阶段。利用分子群体遗传学，将分析美国豌豆蚜虫种群之间的地理差异以及物种形成过程中基因组差异的异质性。在关键的细节被时间的流逝所掩盖之前，这个项目将为物种形成的实际发生提供高分辨率的图片。豌豆蚜虫是一种引进的农业害虫。这些结果不仅阐明了基本的进化过程，而且为其他入侵类群的进化研究提供了一个模型。学生和博士后将接受综合研究方法的培训，该方法跨越了生态学、微进化学和系统学之间的传统科学界限。该项目开发的独特遗传和生态工具将被越来越多的研究豌豆蚜虫遗传学的科学家广泛使用，豌豆蚜虫是基因组测序的新目标物种之一。最后，PI用她的研究来告知她广泛的努力，以教育更广泛的社区关于进化生物学。

Sometimes, populations within a species begin to utilize different resources or habitats. Over time, these populations will diverge genetically if specialists on one of the possible resources leave more offspring than do more generalized individuals. If this specialized resource use alters the pattern of mate choice such that individuals tend to mate with others utilizing the same resource or habitat, these divergent populations are likely to become two different species. Although the many products of speciation in the distant past are clearly visible in the millions of species on Earth, reconstructing the process of speciation as it occurs within diverging populations is difficult because important clues to the processes disappear after speciation is complete. First, diverging populations in different geographic locations experience natural selection on the various resources semi-independently-- they may approach speciation at different rates or even evolve toward different outcomes. Secondly, some genes within incipient species diverge very rapidly under the divergent natural selection, and patterns of molecular variability at these genomic regions tell the genetic story of speciation. However, these unique patterns are obscured over time, and eventually all genes will tell the same story, so analyses of anciently diverged species cannot identify the crucial genetic changes that drive the process. Here, a well-studied set of populations of an insect species (the pea aphid) that are specialized on different host plants will be used to capture a glimpse of the early stages of speciation. Using molecular population genetics, both geographic differences between pea aphid populations across the US and the heterogeneity of divergence across the genome during speciation will be analyzed. This project will provide a high-resolution picture of speciation as it actually occurs, before crucial details are obscured by the passage of time.The pea aphid is an introduced agricultural pest. These results will not only illuminate basic evolutionary process, but will serve as a model for the study of evolution in other invasive taxa. Students and postdoctoral associates will be trained in an integrative research approach that crosses traditional scientific boundaries between ecology, microevolution and systematics. The unique genetic and ecological tools developed in this project will be widely used by members of a growing consortium of scientists working on pea aphid genetics, which is one of the species newly targeted for genome sequencing. Finally, the PI uses her research to inform her extensive efforts to educate the broader community about evolutionary biology.